The present invention relates to an improved electric contact structure as well as a relay and a switch which use the same, and more particularly to a small-size relay and a small-size switch operable with a relatively small current for communication devices.
In recent years, the requirements for scaling down electric or electronic devices and possible reductions in power consumption thereof have been on the increase. In this circumstances, the requirement for scaling down a relay or a switch to be mounted on a printed board for a communication device and also for improvement in sensitivity thereof have also been on the increase. The small-size relay or switch needs a small contact force or a small contact pressure. It is particularly important to keep a stability of an initial contact resistance. To keep the stability of the initial contact resistance, it is preferable that a contact surface layer is made of a soft metal.
The relay and switch are placed in a part such as a cover made of a plastic material, whereby the contact surface layer is exposed to an organic gas atmosphere. The relay and switch may receive an external load. The material for the contact surface layer is required to have a stable surface state in order to ensure a good contact resistance under various conditions.
It has been known in the art to which the present invention pertains that Au and an AuAg alloy are soft and stable in surface state as well as show a high conductivity. Au and AuAg are so soft as showing a plastic deformation. This plastic deformation may cause a possible adhesion of the contact surface with an opposite contact surface. The adhesion of the contact surface with the opposite contact surface may cause the loss of reliability.
A development of the contact surface layer material having an anti-adhesion property has been made. In Japanese laid-open patent publication No. 6-108181, it is disclosed that 1-10% by weight of Pd and 10-100 ppm of C are added to Au or the AuAg alloy to prepare the contact surface layer material, so that the electric contact superior in anti-adhesion property and contact stability is obtained.
In Japanese laid-open patent publication No. 6-325650, it is disclosed that an AuNi alloy, an AuPd alloy or an AuAgPt alloy is used for contact surface layers of confronting contacts in order to obtain an anti-adhesion property and a contact stability.
The adhesion between the soft metal contact surface layers of the contacts may be caused both in operating state of the electric contacts and in receipt of external shock or vibration during non-operating state. The above Japanese publication addresses that the anti-adhesion property is improved but only in operating state. The above soft metal materials have a problem that upon receipt of external vibration or external shock in non-operating state or upon application of vibration due to ultrasonic cutter, an adhesion of a break contact, which is in contact with a counterpart contact surface in closed-state, may be caused, whereby it is difficult to enter the contact into opening state, wherein the break contact is separated from the counterpart contact surface whilst a make contact is in contact with another counterpart contact surface. A probability of appearance of adhesion of the contact surfaces is increased as a content of Au in the contact surface layer is high. It is effective to reduce the content of Au in the contact surface layer for improvement in the anti-adhesion property. This reduction in reduce the content of Au causes another problem with reducing the stability of the contact resistance. Consequently, it is difficult for the above conventional technique to obtain both the high anti-adhesion property and the highly stable contact resistance.
Furtber, if the alloy of the contact surface layer includes Ni, still another problem is caused in a segregation of Ni, whereby it is difficult to obtain a stability of the contact resistance.
In the above circumstances, it had been required to develop a novel electric contact surface structure free from the above problem.